1. Field of the Invention
The present invention relates to an ink jet apparatus utilizing volume expansion caused by evaporation heated of ink.
2. Description of the Related Art
Recently, a printer using an ink jet apparatus is widely utilized as an output printer for an office computer because of its silent printing operation.
A conventional ink jet apparatus is described hereinafter.
FIG. 6 schematically illustrates a conventional ink jet printer. In FIG. 6, numeral 1 denotes an ink reservoir for storing electrical conductive ink, 2 an ink tank for supplying the conductive ink to the ink reservoir 1, and 3 a nozzle having an opening formed in part of a wall forming the ink reservoir 1. Numerals 4 and 5 denote a pair of electrodes fixedly mounted on part of the wall forming the ink reservoir 1, and 6 a power supply connected to the electrodes 4 and 5.
Operation of the ink jet apparatus having the above structure is described hereinafter.
When a voltage of the power supply 6 is applied between the electrodes 4 and 5, a current flows through the conductive ink between the electrodes 4 and 5. The conductive ink between the electrode 4 and 5 is heated and partially evaporated to produce bubbles, so that volume of the ink expands sharply and the conductive ink within the reservoir is pressurized. The conductive ink is jetted or spouted out from the nozzle 3 by the pressure thereof. When the application of the voltage from the power supply 6 is stopped, the bubbles produced in the conductive ink disappear rapidly since an amount of heat of the bubbles is taken by the conductive ink around the bubbles, so that pressure within the ink reservoir becomes negative and the ink jet stops.
With the conventional structure described above, however, when a DC power supply is used as the power supply, the direction of current flowing between the electrodes is fixed and the conductive ink is electrolyzed at the electrodes, so that deposits are formed at the electrodes and the electrodes are deteriorated. Accordingly, the shape of the electrodes can not be kept uniform. Further, when an AC power supply is used as the power supply, the electrolysis between the electrodes can be prevented. However, since an instantaneous value of AC signal is always varied as shown by (a) of FIG. 7, a temperature Te of the ink is varied unevenly as shown by (b) of FIG. 7 in synchronism with the absolute value of the current I flowing between the electrodes by the AC power supply. Since an amount of heat for heating the conductive ink is larger than an amount of heat absorbed into the surrounding conductive ink when the instantaneous current is large, the temperature of the ink is increased. However, when the instantaneous current is small, an absorption rate of the heat into the surrounding conductive ink is higher than a rate of heating the conductive ink. Accordingly, even if the temperature Te of the conductive ink becomes higher than a jet temperature Fu and the ink jet starts at time A, since an ink temperature Te varies around the jet temperature Fu due to variation of the instantaneous value of current, the ink is jetted or spouted out with small drops of particles many times. Accordingly, the ink is flown about or scattered and a stable ink jet cannot be obtained.